Power amplifiers (PA) may be used in various applications, such as in broadcast equipment for wireless communication. The broadcast equipment may be contained in base transceiver station (BTS) or user equipment (UE) or other transceiver equipment used for wireless mobile communications, such as in LTE, WiMax, WiFi, CDMA, GSM, EDGE, and UMTS standards.
Power amplifiers for power amplifying input signals may ideally produce output signals that are linear amplification of the input signals. However, power amplifiers in applications would have distortions due to nonlinear properties, or nonlinearities in the power amplifiers. In order to reduce such distortions in the output signals, the nonlinearities in the power amplifiers may need to be compensated.
For example, a typical power amplifier in a BTS may represent a significant portion of the cost and power demand of the BTS, for example, 30% of total power demand and 30% of the cost. A typical power amplifier may have one or more zone of nonlinearity, and the nonlinear behavior of the typical power amplifier may be affected by various factors such as power supply, temperature, gain setting, etc. Nonlinearity in the power amplifier may degrade error vector magnitude (EVM), which is used to quantify the performance of a radio transmitter or receiver, and increase spectral regrowth, which is the spreading of signal bandwidth due to distortions. Typically, only nonlinearities in the backend components near the output, i.e. radio frequency (RF) distortions, are considered for compensation. However, nonlinearities may also occur near the frontend, i.e. baseband nonlinear distortions. In the frontend circuit paths, the nonlinearity in the in-phase signal path may be different from the nonlinearity in the quadrature-phase signal path.
Thus, there is a need for improved power amplifiers that compensates for baseband nonlinearity.